Thermoformable acoustic product

ABSTRACT

A thermo-formed acoustic product formed from an acoustic sheet with a relatively high flow resistance, and a layer of porous flow resistive spacer material attached to one side of the acoustic sheet and having a flow resistance substantially smaller than the acoustic sheet. The acoustic product has locally reactive acoustic behavior and an overall air flow resistance of between 2800 Rayls and 8000 Rayls. A decorative facing can be applied to the acoustic sheet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to materials for sound absorption. Moreparticularly it relates to thermo-formable acoustic products that haveenhanced sound absorption properties and can be decoratively faced.

2. Description of the Related Art

Sound absorption provides a useful means for noise reduction in a widevariety of industrial, commercial, and domestic applications. To achievethe optimum degree of sound absorption, it is desirable to use acomposite assembly of different layers, such that the maximum soundabsorption is achieved in the minimal possible space, with the lowestpossible mass appropriate for the application.

The sound absorption of a porous material is known to be a function offundamental material properties, including thickness, air flowresistance, mass, stiffness, porosity, tortuosity etc, and applicationparameters, such as any air space behind the material, or alternatively,the acoustic and mechanical properties of any other material situatedbehind the porous material, such as a spacer layer, an isolation layer,or acoustic underlay.

Adding a third dimension to a sound absorbing assembly providesaesthetic and practical physical properties such as stiffness andconformance to contoured shapes, such as found in motor vehicle trim,such as, for example, for the floorpan, firewall, trunk, or parcelshelf.

In many of these applications it is desirable that the sound absorbingcomposite should have a decorative finish that does not detract from thesound absorption. Even more desirably, the decorative facing should haveproperties that actually enhance the sound absorption by becoming anintegral component of the sound absorbing composite assembly. In certainapplications, such as a motor vehicle floor assembly, it is desirablethat the composite conforms to the shape of a surface, for example, orotherwise retains a particular shape, for example as an aestheticfeature for wall decoration.

In other applications it is desirable that the sound-absorbing compositeshould have sufficient strength that it can support light loads andresist mechanical damage.

In such applications it is desirable that the sound absorbing assembly,and any decorative facing, can be heat molded to the required shape in asimple and cost effective process.

The applicant is the applicant for Australian Patent Application No.48754/00, which describes a Pinnable Acoustic Panel, comprising adecorative layer, a high flow resistive layer and a foam spacer layer.The high flow resistive layer has sufficient stiffness and density thatit will retain pins used to attach papers and such to the panel. Thecontent of this is incorporated herein by cross-reference. The applicantis also the applicant in respect of PCT/AU01/00880, which discloses athermoformable acoustic sheet, the content of which is also incorporatedherein by cross-reference.

Applications for a sound absorbing composite assembly include, but arenot limited to, interior insulation for motor vehicles, and commercialdecorative wall, ceiling, and floor finishes. In most instances, adecorative facing is required for aesthetic purposes or for mechanicalprotection.

Flow resistive thermo-formable materials have been provided, howeversuch prior art does not address the practicality of achieving aneffective sound absorbing solution. In particular, environmental,manufacturing and cost issues are a concern, whilst retaining theability to vary the mechanical properties and maintaining or enhancingthe sound absorbing properties of the product and combining this withthe aesthetic quality of the product.

In some cases a decorative layer may also be included on, or attachedto, the flow resistive thermo-formable material. However theseapplications similarly do not address the practicality of achieving aneffective sound absorbing solution as discussed above.

Hence, it is an object of this invention to provide a thermo-formableacoustic product with enhanced acoustic properties, and a method ofproducing such a product that will overcome or at least ameliorate thedisadvantages of the prior art or at least provide a useful alternative.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention provides a thermo-formed acousticproduct formed from an acoustic sheet with a relatively high flowresistance, and a layer of porous flow resistive spacer materialattached to one side of the acoustic sheet and having a flow resistancesubstantially smaller than the acoustic sheet, wherein the acousticproduct has locally reactive acoustic behavior and an overall flowresistance of between 2800 Rayls and 8000 Rayls.

Preferably the acoustic sheet has a favorable aesthetic appearance. Inone embodiment, the acoustic sheet is a decorative layer, such as acarpet, textile or other permeable film facing. In another embodiment,the acoustic sheet is formed by a decorative layer and at least oneadditional flow resistive layer.

Preferably, the porous flow resistive spacer material is a fibrous web.Even more preferably, the fibrous web spacer material has avertically-lapped construction so that the fibers are oriented in aplane normal to that of the acoustic sheet.

It is also preferable that the fibers of the fibrous web spacer materialare at least partially thermally bonded together.

It is also preferable that the fibrous web spacer material is thermallymolded. The molding can be to a final shape or an intermediate shape forfurther molding or processing.

Preferably, in one aspect the fibrous web spacer material is formed fromhigh melt and low melt fibers. Preferably, the low melt fibers are abi-component fiber. In another preferred aspect the low melt fibers area mono-component fiber.

Preferably, in another aspect the acoustic sheet includes a flowresistive layer formed from high melt and low melt fibers. Preferably,the flow resistive layer is compressed to give the desired air flowresistance. Even more preferably, the low melt fibers are selected tohave a temperature resistance that is applicable to the intended use.

Preferably, the thermo-formed acoustic product has a total air flowresistance of between 3000 Rayls to 5000 Rayls. More preferably, thethermo-formed acoustic product has a total air flow resistance ofbetween 3200 Rayls to 4500 Rayls.

Preferably, the fibrous web spacer material has an air flow resistanceof between 100 Rayls to 800 Rayls. Even more preferably, the fibrous webspacer material has an air flow resistance of between 200 Rayls to 400Rayls.

Preferably, the fibrous web spacer material has a density of 150-2000g/m². The density of the fibrous web spacer material is determined bythe specific acoustic and physical properties desired of the overallsystem. Preferably, the acoustic sheet has a density of 150-2000 g/m².The density is selected on the basis of the acoustic and physicalproperties desired of the overall system.

Preferably, the thermo-formed acoustic product can be used for amultiplicity of purposes, including, but not exclusive to insulation formachinery and equipment, motor vehicle insulation, domestic applianceinsulation, dishwashers and commercial wall and ceiling panels.

Preferably, the acoustic product has a sag resistance to temperatures ator about 150° C. For example in automotive engine bay applications thepart should exhibit minimal sag at operating temperatures.

In another aspect, the present invention is a method of forming athermo-formed acoustic product formed from an acoustic sheet with arelatively high flow resistance, and a layer of porous flow resistivespacer material attached to one side of the acoustic sheet and having aflow resistance substantially smaller than the acoustic sheet, includingthe steps of heating the porous flow resistive layer and acoustic sheet,and molding the acoustic sheet and porous flow resistive layer whereinthe acoustic product has locally reactive acoustic behavior and anoverall air flow resistance of between 2800 Rayls and 8000 Rayls and theporous flow resistive spacer material attached to one side of theacoustic sheet.

In one embodiment porous flow resistive spacer material is attached toone side of the acoustic sheet during molding. In another embodiment theporous flow resistive spacer material is attached to one side of theacoustic sheet prior to molding. Preferably the porous flow resistivespacer material is laminated to the acoustic sheet prior to beingmolded.

In one embodiment the acoustic sheet and porous flow resistive layer aresupplied to the molding process in roll form. Alternatively, theacoustic sheet and porous flow resistive layer are supplied to themolding process in sheet form.

In one embodiment, the acoustic product is molded in a cold moldingtool. In this embodiment it is preferable that a thermo-formed acousticproduct is formed by a flow resistive spacer material having crystallinefibers.

In another embodiment, the acoustic product is molded in a hot moldingtool. In this embodiment it is preferable that a thermo-formed acousticproduct is formed by a flow resistive spacer material having amorphousfibers.

Preferably the heating the acoustic product is achieved with infraredradiation, hot air, or a combination of hot air and infra red radiation.

In another aspect the acoustic product is formed from predominantly onepolymer type. Preferably, the acoustic product is formed predominantlyfrom polyester fibers or polypropylene fibers.

In another aspect the acoustic properties of the acoustic product areassisted by the three-dimensional geometry of the molded product.

The present invention, as detailed above, provides the advantages of amulti-purpose clean, energy efficient, low cost, recyclable material asa thermo-formable acoustic sheet with enhanced and consistent acousticalproperties while providing a favorable aesthetic appearance in preferredembodiments. A further advantage is that the present invention providesan insulation that provides a lower resonance than current systems, hassuperior resilience and predictable mechanical properties.

A further advantage of the above process is that the product is formedin a fast cycle time, to provide cost-effective solutions for use as aninsulation in original equipment, such as motor vehicles anddishwashers, wall and ceiling linings and other industrial commercialand domestic purposes.

It is a further advantage of this invention to produce an enhancedthermo-formable acoustic product with less energy than conventionalsystems, providing an improved environmental outcome.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only,with reference to the accompanying drawings.

FIG. 1. Schematic illustration of one embodiment of the thermo-formedacoustic product according to the present invention.

FIG. 2. Schematic illustration of another embodiment of thethermo-formed acoustic product according to the present invention.

FIG. 3. Schematic illustration of another embodiment of thethermo-formed acoustic product according to the present invention.

FIG. 4. Schematic illustration of an embodiment of the thermo-formedacoustic product according to the present invention.

FIG. 5. Schematic illustration of an embodiment of the thermo-formedacoustic product according to the present invention.

FIG. 6. A plot of transmission loss versus frequency for the compositeformed in Example 1.

FIG. 7. A plot of sound absorption coefficient versus frequency for thecomposite formed in Example 1.

FIG. 8. A plot of sound absorption coefficient versus frequency fordifferent average fiber size with a fiber blend of 600 gsm.

FIG. 9. A plot of sound absorption coefficient versus frequency for twosamples having a 23 mm thick spacer layer and a 13 mm thick spacerlayer.

FIG. 10. A plot of transmission loss versus frequency for two sampleshaving a 23 mm thick spacer layer and a 13 mm thick spacer layer.

FIG. 11. A plot of stiffness and loss factor versus density for sampleswith 2.5 denier average fiber size.

FIG. 12. A plot of stiffness and loss factor versus density for sampleswith 3.7 denier average fiber size.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with reference to preferredembodiments. It should be understood that the below described a limitednumber of embodiments of the invention and modifications can be madewithout departing from the scope of the invention.

In certain circumstances, the actual sound absorption achieved in apractical example of application can be less than that inferred fromlaboratory testing. This has been shown to result from the effect ofsound transmission behind and parallel to the sheet. In acoustic terms,this material is installed in a non-locally reactive situation.

Those familiar with the concepts of flow resistive screens as soundabsorption media, will appreciate that the acoustic performance achievedin real life will be superior in the event that the installation allowsthe thermo-formable acoustic sheet to behave in a locally reactivemanner.

Referring to FIG. 1, in one embodiment of the present invention athermo-formable acoustic product 1 is shown which is formed from anacoustic sheet 2, and a layer of porous flow resistive spacer material4. The product is typically applied to a surface 5, usually conformingto that shape. The acoustic sheet 2 has a favorable aesthetic appearanceby virtue that the acoustic sheet is a decorative layer, such as acarpet. Alternatively the acoustic sheet 2 can be a flow resistive layeronly where a favorable aesthetic appearance is not required.

Referring to FIG. 2, in another embodiment of the present invention athermo-formable acoustic product 6 is shown which is formed from adecorative layer 9, a compressed flow resistive acoustic layer 7, and alayer of porous flow resistive spacer material 10. The product istypically applied to a surface 11, usually conforming to that shape.

The decorative layer may be an automotive carpet, or a commercialtextile. In one embodiment, the decorative layer is a decorative fabricwhich has been previously coated with an adhesive resin so as to bindthe fibers and to control the air permeability. Such a coating may beapplied in any of the well-known means of coating textiles. The coatingis preferably a thermoplastic adhesive powder, web or film, extrudedthermoplastic resin or a liquid coating. The coating process must befinely controlled so as to ensure a consistent and even coating of thedecorative fabric and a pre-determined air flow resistance, and hencethe performance of the decorative layer as an element of the acousticproduct.

The flow resistive compressed acoustic sheet 7 is formed by a similarprocesses as described in PCT/AU01/00880, and has an air flow resistancein the range of 2800-7000 mks Rayls, more preferably in the range3000-5000 mks Rayls and even more preferably in the range of 3200-4500mks Rayls.

In PCT/AU01/00880, the preferred flow resistance range is limited by thepractical application of the product, however the preferred range offlow resistance for the enhanced thermoformable acoustic sheet has beenselected to provide the optimum acoustic properties for the intendedapplications. The increased flow resistance is achieved by increasingthe compaction density and further reducing the volume of theinterstatial spaces within the acoustic sheet. This is achieved throughcontrolling the process parameters of time, temperature and pressure,applied to the fibrous web during manufacture of the acoustic sheet. Inaddition, it has also been found that further optimisation of the fiberblend, and web density, makes it possible to achieve a flow resistancein the preferred range.

For practical purposes, the product must have a temperature resistanceappropriate for the intended application. For certain automotiveapplications, the sheet must have a low sag modulus at temperatures upto about 150° C.

The product can be formed into a three dimensional shape, so providingan air space and structural rigidity. Such a shape can also formpartially enclosed cells, such as a honeycomb, or egg-carton typestructure, that will provide local reactivity and increase theacoustical performance of the thermo-formed acoustic product.

The sheet 7 is produced from a fibrous web of 150-2000 g/m². It is clearthat for cost minimisation, the lowest practical web weight is desired.The web is compressed by between 15 and 25 times. The thickness of theweb has an influence on the air flow resistance, however the inventorshave demonstrated through modelling and practice, that the desiredacoustic properties can be achieved through a combination of differentfiber selections and ratios, thicknesses and processing conditions.

The flow resistive material 10 is produced in planar form and may bepresented as a roll or as a sheet. In one form of the invention, theflow resistance of the material can be achieved or enhanced through theapplication of an adhesive resin. The resin may be applied in a powder,fiber or film form, preferably in a dry lamination or coating process.

The resin can be selected from a range of thermoplastic, or thermoset,polymers. Preferred thermoplastic resins include, but are not limitedto, polyester and polyproylene.

From a cost perspective, the selection of resin and fiber will often bedetermined by the lowest possible cost to achieve the appropriate levelof acoustic and physical performance.

In a preferred embodiment, the thermo-formable acoustic product isproduced from one individual polymer system so that it can be readilyrecycled, in particular polyester or polypropylene.

The web of fibrous material used to produce the flow resistive acousticsheet 7 is preferably produced from a vertically-lapped web of high loftthermally bonded material as produced by the vertical-lapping process,known as the STRUTO process under Patent WO 99/61963, although otherprocesses for producing a vertically, or rotary, lapped web would alsobe suitable. Suitable low and high melt materials can be used as therespective fibers, which can of mono- or bi-component form. Alternativeweb forming systems, such as cross-lapping, air laid, and needlepunching can also be used, however these have been found to result in aweb with less consistent acoustic properties. The web is consolidated byheating and compressing, as described in PCT/AU01/00880.

As an extension of prior art revealed in PCT/AU01/00880, theconsolidation of the fibrous web can be conducted as an in-line processimmediately following production of the fibrous web. The fibrous web ispreferably formed as previously described by the vertical lappingprocess, but other web forming processes, such as cross-lapping, and/orneedle punching and/or thermal bonding can also be used. A moreconsistent acoustic performance is obtained through the vertical lappingprocess.

A flow resistive screen does not behave in a locally reactive mannerunless the air space behind the screen provides some acoustic impedance.To induce locally reactive behavior in the thermo-formed acousticproduct, it is necessary to insert a flow resistive material into theair space, or alternatively to break up the air space into a cellular orhoneycomb structure as previously described.

As a preferred embodiment, a vertically lapped fibrous web is used as aflow resistive spacer material to fill the void created by the airspace, however other forms of porous materials can also serve thispurpose, for example polyurethane foam, needle punched fibrous webs or across lapped thermally bonded fibrous webs. The mechanical andacoustical properties of the spacer material are critical to ensuringthe optimum acoustic performance of the composite.

The fibrous web spacer material can be attached to the thermo-formableacoustic sheet by lamination or by mechanical means, for exampleriveting, coupling or plastic welding. In one embodiment, an adhesive 3,8 may also be used between the acoustic sheet and the fibrous web spacermaterial.

Where a powder adhesive has been used to control the flow resistance ofthe sheet 7, this adhesive can be heat reacted to act as an adhesive forthe fibrous web spacer material. This can be achieved through contactheating, hot air impingement, or indirect heating, such as infrared, orother similar means.

Where the adhesive system that controls the flow resistance of the sheetis in the fibrous form, it may be advantageous to use an additional hotmelt adhesive in powder, web, film or similar form. The use of such anadhesive layer can also be used to control the final flow resistance ofthe sheet and fibrous web spacer material composite.

The fibers selected for fibrous web spacer material influence the finalacoustic properties significantly. Accordingly the fibrous web spacermaterial is preferably formed from fibers within the range of 0.5 to 6denier, preferably 0.5 to 3 denier, and more preferably from 0.5 to 1denier. These fiber sizes are nominated on the basis of staple fiber,however the melt blown process can produce fibers in even smallerdeniers, producing higher flow resistance and an even more beneficialresult.

Of course, it is understood that the denier of a fiber relates to themass per 9000 m of fiber. A polymer with a low specific gravity willhave more fibers per unit of mass, and volume for a given mass.Accordingly, a low density polymer, such as polypropylene will have morefibers, at the same denier, than the equivalent mass of say polyesterfiber. In this event a fibrous web spacer material produced from a lowdensity polymer, such as polypropylene is a preferred form of thisinvention.

The thermo-formed acoustic product is formed by heating the acousticsheet and porous layer, and molding them to a desired three dimensionalshape. After molding, the acoustic sheet is attached to the porous layerto form an integral acoustic product. The three dimensional shape couldbe an intermediate shape or a final shape. The heating of the acousticsheet and porous layer can be conducted before or during molding.

Where the porous layer is laminated to the acoustic sheet, it ispossible to also thermoform the spacer material in the same process. Inthis event the spacer material can be selected from a fibrous webcomprising fibers with an appropriately selected melting range.Alternatively, the porous layer may consist of fibers with asubstantially higher melting range than the thermo-formable acousticsheet, and may remain unaffected by the molding process. Attachment ofthe porous layer may be achieved by lamination as described, or bymechanical means, such as staples or other form of mechanical fastener.

The spacer material may optionally be placed into the molding tool priorto the placement of the heated acoustic sheet into the molding tool. Theheat retained in the sheet is often sufficient to cause adhesion to thepieces placed into the mold, however an adhesive layer may be requiredfor more secure adhesion. As a further variation on this flexibleprocess, sheets or pieces of porous layer may be separately adhered tothe thermoformed sheet, after the molding process. Once again thesepieces may be adhesively or mechanically secured. In some cases thepieces may be installed independently onto the panel to which thethermoformed acoustic sheet is attached.

For applications requiring low sag at elevated temperature, for examplethose found in engine bays of motor vehicles, of the thermo-formedacoustic product, the selection of the fibers used to form the fibrousweb spacer material is important. When the acoustic product is formed ina cold, or cool mold, crystalline fibers have been found to increase thesag resistance compared to amorphous fibers. When the acoustic productis formed in a hot mold, amorphous fibers have been found to increasethe sag resistance compared to crystalline fibers.

The fibrous web spacer material of the preferred embodiment haspreviously been described as a vertically lapped, thermally bondednon-woven produced by the STRUTO, or other, process. When this fibrousweb spacer material is thermoformed with, or without, thethermo-formable acoustic sheet, the vertical fibers adopt av-orientation by flexing at the centre-line of the web. Alternativelythe fibers may adopt a z-orientation, by flexing at the outer layers ofthe web. In both instances, this results in a change in the mechanicalproperties of the web, making it behave more effectively as a spring,improving resilience and resulting in a lower cut-off frequency.

As shown in FIG. 3, in another embodiment of the present invention athermo-formable acoustic product 12 is shown which is formed from adecorative layer 13, a compressed flow restive acoustic layer 15, alayer of porous flow resistive spacer material 17, and a second flowresistive acoustic sheet 19 may also be used to further mechanicallystabilise the product, or assist in the attachment to another surface20. The surface may also have holes 21. As with the previousembodiments, an adhesive layer 14, 15 and 18 may also be provided toassist attachment.

Referring to FIG. 4, in another embodiment of the present invention athermo-formable acoustic product 28 is shown which is formed from adecorative layer 22, a compressed flow resistive acoustic layer 24, anda layer of porous flow resistive spacer material 26 and adhesive layers23 and 24 between those layers. The product is applied to a surface 27,conforming to that shape.

Referring to FIG. 5, in another embodiment of the present invention athermo-formable acoustic product 35 is shown which is formed from adecorative layer 29, a compressed flow resistive acoustic layer 30, anda layer of porous flow resistive spacer material 31 and adhesive layers32 and 33 between those layers. The product is thermo-formed to conformthe shape of the surface 34.

The following examples are provided exemplary examples of preferredembodiments of the present invention.

EXAMPLE 1

A compressed flow resistive sheet comprising both high melt and low meltbicomponent polyester fibers was formed in accordance withPCT/AU01/00880. The sheet comprised 70% 4 denier low melt bicomponentfibers, and 30% 6-denier high melt polyester staple fibers. The totalmass of the flow resistive sheet was 1000 g/m².

A vertically-lapped spacer web made from 30% 2-denier bicomponentpolyester fibers, 20% 12-denier and 50% 6-denier polyester staple fiberswas laminated to the flow resistive sheet with heat reactivated hot meltpowder applied at a rate of 30 g/m². The total mass of the spacer layerwas 800 g/m².

The resultant product had a total flow resistance of 3200 Rayls and was23 mm thick.

The composite was tested in an alpha cabin, using Toyota testspecification TSL 0600G—Test method for acoustic materials, for soundabsorption and transmission loss and the results were compared with atarget specification based on the prior art, with the same total mass.The product of the current invention demonstrated improved low frequencysound absorption as shown in FIG. 7 and a higher transmission loss asshown in FIG. 6.

EXAMPLE 2

Three samples of spacer layers similar to the spacer layer formed inExample 1 were formed using 2.5, 3.7 and 6 denier average fiber sizeexcept that the spacer layer had a total mass of 600 gsm. A plot of thesound absorption coefficient versus frequency of the three samples isshown in FIG. 8.

EXAMPLE 3

A similar product was formed to the product formed in Example 1 exceptthat the spacer layer was 13 mm thick and had a total mass of 400 gsm.FIGS. 9 and 10 show the effect of the thickness of the spacer layer onthe sound absorption coefficient and the transmission loss atfrequencies between 200 Hz and 6300 Hz.

EXAMPLE 4

A similar product was formed to the product formed in Example 2 exceptfour samples having densities of 400, 600, 800 and 1000 grams per squaremeter were formed using a blend of fibers having a 2.5 denier averagefiber size. The dynamic properties of stiffness and loss factor weremeasured for each sample and a plot of stiffness and loss factor versusdensity appears as FIG. 11.

EXAMPLE 5

A similar product was formed to the product formed in Example 2 exceptfour samples having densities of 400, 600, 800 and 1000 grams per squaremeter were formed using a blend of fibers having a 3.7 denier averagefiber size. The dynamic properties of stiffness and loss factor weremeasured for each sample and a plot of stiffness and loss factor versusdensity appears as FIG. 12.

The foregoing describes only certain embodiments of the invention andmodifications can be made without departing from the scope of theinvention.

1. A thermo-formed acoustic product formed from an acoustic sheet with arelatively high flow resistance, and a layer of porous flow resistivespacer material attached to one side of the acoustic sheet and having aflow resistance substantially smaller than the acoustic sheet, whereinthe acoustic product has locally reactive acoustic behavior and anoverall air flow resistance of between 2800 Rayls and 8000 Rayls.
 2. Athermo-formed acoustic product according to claim 1 wherein the acousticsheet has a favorable aesthetic appearance.
 3. A thermo-formed acousticproduct according to claim 2 wherein the acoustic sheet is a decorativelayer, such as a carpet, textile or a fabric facing.
 4. A thermo-formedacoustic product according to claim 3 wherein the decorative layer isselected from the group consisting of a carpet, a textile and apermeable film facing.
 5. A thermo-formed acoustic product according toclaim 2 wherein the acoustic sheet includes a decorative layer and atleast one additional flow resistive layer.
 6. A thermo-formed acousticproduct according to claim 1 wherein the porous locally reactive flowresistive spacer material is a fibrous web.
 7. A thermo-formed acousticproduct according to claim 6 wherein the fibrous web spacer material hasa vertically-lapped construction so that the fibers are oriented in aplane normal to that of the acoustic sheet.
 8. A thermo-formed acousticproduct according to claim 7 wherein the fibers of the fibrous webspacer material are at least partially thermally bonded together.
 9. Athermo-formed acoustic product according to claim 8 wherein the fibrousweb spacer material is formed from high melt and low melt fibers.
 10. Athermo-formed acoustic product according to claim 9 wherein the low meltfibers are a bi-component fiber.
 11. A thermo-formed acoustic productaccording to claim 9 wherein the low melt fibers are a mono-componentfiber.
 12. A thermo-formed acoustic product according to claim 1 whereinthe acoustic sheet includes a flow resistive layer formed from high meltand low melt fibers.
 13. A thermo-formed acoustic product according toclaim 12 wherein the flow resistive layer is compressed to give thedesired air flow resistance.
 14. A thermo-formed acoustic productaccording to claim 12 wherein the low melt fibers are selected to have atemperature resistance that is applicable to the intended use.
 15. Athermo-formed acoustic product according to claim 1 wherein thethermo-formed acoustic product has an overall air flow resistance ofbetween 3000 Rayls to 5000 Rayls.
 16. A thermo-formed acoustic productaccording to claim 15 wherein the thermo-formed acoustic product has anoverall air flow resistance of between 3200 Rayls to 4500 Rayls.
 17. Athermo-formed acoustic product according to claim 1 wherein the porousspacer material has an air flow resistance of between 100 Rayls to 800Rayls.
 18. A thermo-formed acoustic product according to claim 17wherein the porous spacer material has an air flow resistance of between200 Rayls to 400 Rayls.
 19. A thermo-formed acoustic product accordingto claim 1 wherein the porous spacer material has a density of 150-2000g/m².
 20. A thermo-formed acoustic product according to claim 1 whereinthe acoustic sheet has a density of 150-2000 g/m².
 21. A thermo-formedacoustic product according to claim 1 wherein the acoustic product has asag resistance to temperatures at or about 150° C.
 22. A method offorming a thermo-formed acoustic product formed from an acoustic sheetwith a relatively high flow resistance, and a layer of porous flowresistive spacer material attached to one side of the acoustic sheet andhaving a flow resistance substantially smaller than the acoustic sheet,including the steps of heating the porous flow resistive layer andacoustic sheet, and molding the acoustic sheet and porous flow resistivelayer wherein the acoustic product has locally reactive acousticbehavior and an overall air flow resistance of between 2800 Rayls and8000 Rayls and the porous flow resistive spacer material is attached toone side of the acoustic sheet.
 23. A method of forming a thermo-formedacoustic product according to claim 22 wherein the porous flow resistivespacer material attached to one side of the acoustic sheet duringmolding.
 24. A method of forming a thermo-formed acoustic productaccording to claim 22 wherein the porous flow resistive spacer materialattached to one side of the acoustic sheet prior to molding.
 25. Amethod of forming a thermo-formed acoustic product according to claim 24wherein the porous flow resistive spacer material is laminated to theacoustic sheet prior to being molded.
 26. A method of forming athermo-formed acoustic product according to claim 22 wherein theacoustic sheet and porous flow resistive layer are supplied to themolding process in roll form.
 27. A method of forming a thermo-formedacoustic product according to claim 22 wherein the acoustic sheet andporous flow resistive layer are supplied to the molding process in sheetform.
 28. A method of forming a thermo-formed acoustic product accordingto claim 22 wherein the acoustic product is molded in a cold moldingtool.
 29. A thermo-formed acoustic product formed by the method of claim28 wherein fibers used to form the flow resistive spacer material arecrystalline fibers.
 30. A method of forming a thermo-formed acousticproduct according to claim 22 wherein the acoustic product is molded ina hot molding tool.
 31. A thermo-formed acoustic product formed by themethod of claim 30 wherein fibers used to form the flow resistive spacermaterial are amorphous fibers.
 32. A method of forming a thermo-formedacoustic product formed according to claim 22 wherein heating theacoustic product is achieved with infra red radiation, hot air, or acombination of hot air and infra red radiation.
 33. A thermo-formedacoustic product according to claim 1 wherein the acoustic product isformed from predominantly one polymer type.
 34. A thermo-formed acousticproduct according to claim 33 wherein the acoustic product is formedpredominantly from polyester fibers or polypropylene fibers.